U.S. patent application number 09/917568 was filed with the patent office on 2003-01-30 for article having a protective coating and an iridium-containing oxygen barrier layer.
Invention is credited to Darolia, Ramgopal.
Application Number | 20030022016 09/917568 |
Document ID | / |
Family ID | 25438976 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030022016 |
Kind Code |
A1 |
Darolia, Ramgopal |
January 30, 2003 |
Article having a protective coating and an iridium-containing
oxygen barrier layer
Abstract
A protected article includes a substrate, such as a nickel-base
superalloy, a protective coating comprising aluminum overlying a
surface of the substrate, and an iridium-containing oxygen barrier
layer overlying the protective coating. A ceramic thermal barrier
coating may overlie the protective coating and the oxygen barrier
layer.
Inventors: |
Darolia, Ramgopal; (West
Chester, OH) |
Correspondence
Address: |
GREGORY GARMONG
P.O. BOX 12460
ZEPHYR COVE
NV
89448
US
|
Family ID: |
25438976 |
Appl. No.: |
09/917568 |
Filed: |
July 27, 2001 |
Current U.S.
Class: |
428/633 ;
148/537; 416/241B; 428/652; 428/670 |
Current CPC
Class: |
Y10T 428/12875 20150115;
Y10T 428/12618 20150115; C23C 28/3215 20130101; C23C 28/325
20130101; Y10T 428/12611 20150115; C23C 28/3455 20130101; Y02T
50/60 20130101; C23C 26/00 20130101; C23C 28/345 20130101; Y10T
428/1275 20150115 |
Class at
Publication: |
428/633 ;
416/241.00B; 428/670; 428/652; 148/537 |
International
Class: |
B32B 015/04 |
Claims
What is claimed is:
1. A protected article, comprising: a substrate; a protective
structure overlying a surface of the substrate, the protective
structure comprising a protective coating comprising aluminum and
overlying the surface of the substrate, and an oxygen barrier layer
of an iridium alloy comprising at least about 70 percent by weight
iridium and overlying the protective coating.
2. The protected article of claim 1, wherein the protective coating
is a diffusion aluminide.
3. The protected article of claim 1, wherein the protective coating
is selected from the group consisting of a platinum aluminide and a
nickel aluminide.
4. The protected article of claim 1, wherein the protective coating
is an overlay coating.
5. The protected article of claim 1, wherein the protective coating
further includes a ceramic thermal barrier coating overlying the
protective coating.
6. The protected article of claim 1, wherein the substrate is a
nickel-base alloy.
7. The protected article of claim 1, wherein the substrate is a
nickel-base superalloy.
8. The protected article of claim 1, wherein the oxygen barrier
layer has a thickness of from about 5 micrometers to about 50
micrometers.
9. The protected article of claim 1, wherein the oxygen barrier
layer is an alloy of iridium and elements interdiffused into the
oxygen barrier layer from the substrate and the protective
layer.
10. The protected article of claim 1, wherein the oxygen barrier
layer is an iridium alloy having from about 70 to about 90 percent
by weight iridium.
11. A method of protecting an article, comprising the steps of
providing a substrate including at least a portion of the article;
depositing a protective structure overlying a surface of the
substrate, the protective structure comprising a protective coating
comprising aluminum and overlying the surface of the substrate, and
a layer comprising iridium overlying the protective coating; and
heating the substrate and protective structure to interdiffuse the
protective coating and the layer comprising at least about 70
percent by weight iridium, to form an oxygen barrier layer.
12. The method of claim 11, wherein the step of depositing the
protective structure comprises the step of depositing the
protective coating as a diffusion aluminide.
13. The method of claim 11, wherein the step of depositing the
protective structure comprises the step of depositing the
protective coating from the group consisting of a platinum
aluminide and a nickel aluminide.
14. The method of claim 11, wherein the step of depositing the
protective structure comprises the step of depositing the
protective coating as an overlay coating.
15. The method of claim 11, wherein the step of depositing the
protective structure comprises the step of depositing a ceramic
thermal barrier coating overlying the protective coating.
16. The method of claim 11, wherein the step of providing the
substrate includes the step of providing a nickel-base alloy
substrate.
17. The method of claim 11, wherein the step of heating includes
the step of forming the oxygen barrier layer with a thickness of
from about 5 micrometers to about 50 micrometers.
18. The method of claim 11, wherein the step of heating includes
the step of forming the oxygen barrier layer as an alloy of iridium
and elements interdiffused into the oxygen barrier layer from the
substrate and the protective layer.
19. The method of claim 11, wherein the step of heating includes
the step of forming the oxygen barrier layer having from about 70
to about 90 percent by weight iridium.
Description
[0001] This invention relates to the protection of surfaces from
excessive oxidation using a aluminum-containing protective coating
and, more particularly, to the prevention of excessive oxidation of
the protective coating.
BACKGROUND OF THE INVENTION
[0002] In an aircraft gas turbine Set) engine, air is drawn into
the front of the engine, compressed by a shaft-mounted compressor,
and mixed with fuel. The mixture is burned, and the hot exhaust
gases are passed through a turbine mounted on the same shaft. The
flow of combustion gas turns the turbine by impingement against an
airfoil section of the turbine blades and vanes, which turns the
shaft and provides power to the compressor and fan. In a more
complex version of the gas turbine engine, the compressor and a
high pressure turbine are mounted on one shaft, and the fan and low
pressure turbine are mounted on a separate shaft. The hot exhaust
gases flow from the back of the engine, driving it and the aircraft
forward.
[0003] The hotter the combustion and exhaust gases, the more
efficient is the operation of the jet engine. There is thus an
incentive to raise the combustion and exhaust-gas temperatures. The
maximum temperature of the combustion gases is normally limited by
the materials used to fabricate the turbine vanes and turbine
blades of the turbine, upon which the hot combustion gases impinge.
In current engines, the turbine vanes and blades are made of
nickel-based superalloys, and can operate at temperatures of up to
about 1900-2150.degree. F.
[0004] Many approaches have been used to increase the operating
temperature limits of turbine blades, turbine vanes, and other
hot-section components to their current levels. For example, the
composition and processing of the base materials themselves have
been improved, and a variety of solidification techniques have been
developed to take advantage of oriented grain structures and
single-crystal structures. Physical cooling techniques may also be
used.
[0005] The surfaces of the articles may be protected with an
aluminum-containing protective coating, whose surface oxidizes to
an aluminum oxide scale that inhibits further oxidation of the
surfaces. However, the aluminum oxide scale is relatively permeable
to oxygen. During service, oxygen diffuses from the environment and
through the aluminum oxide scale to the underlying
aluminum-containing protective coating, whereupon more aluminum
oxide is formed. This formation of aluminum oxide is good to a
point, but the formation of too thick an aluminum oxide scale may
lead to spallation of the aluminum oxide scale, consumption of the
aluminum in the aluminum-containing protective coating, and the
loss of protection of the underlying substrate. Excessive diffusion
of oxygen may also lead to excessive oxidation of the underlying
substrate.
[0006] There is therefore a need for an improved approach to the
aluminum-containing protective coatings on surfaces of materials
used at high temperatures, such as nickel-base superalloys. The
present invention fulfills this need, and further provides related
advantages.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention provides a protected article that is
protected both by an aluminum-containing protective coating and a
layer that is highly impervious to oxygen. The aluminum oxide scale
forms on the aluminum-containing protective coating to protect the
underlying substrate. The oxygen barrier layer inhibits further
diffusion of oxygen to the aluminum-containing protective layer, so
that it does not form too thick an aluminum oxide scale, which is
prone to failure by spallation, and is not consumed too rapidly.
The result is a longer-lived protection of the underlying
article.
[0008] A protected article includes a substrate and a protective
structure overlying a surface of the substrate. The protective
structure comprises a protective coating comprising aluminum and
overlying the surface of the substrate, and an oxygen barrier layer
comprising an iridium alloy having at least about 70 percent by
weight iridium and overlying the protective coating. The iridium
alloy preferably has no more than about 90 percent by weight
iridium. The oxygen barrier layer preferably has a thickness of
from about 5 micrometers to about 50 micrometers.
[0009] The substrate is preferably a nickel-base alloy such as a
nickel-base superalloy. The protective coating may be a diffusion
aluminide such as a simple diffusion aluminide, an example being a
nickel aluminide, or a complex diffusion aluminide such as a
platinum aluminide. The protective coating may instead be an
overlay coating such as an MCrAlX overlay coating. A ceramic
thermal barrier coating may overlie the protective coating and the
oxygen barrier layer.
[0010] In this layered system, the aluminum-containing protective
coating oxidizes to form an aluminum oxide scale that protects the
substrate article from excessively rapid oxidation. The
iridium-containing oxygen barrier layer, which may be quite thin
because of the low permeability of oxygen in high-iridium alloys,
inhibits the diffusion of oxygen to and through the aluminum oxide
scale to the underlying protective coating. The result is that the
aluminum oxide scale does not grow too thick or too rapidly, so
that it may continue to protect the surface for extended periods of
time.
[0011] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. The scope of the invention is not, however, limited
to this preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view of a turbine blade;
[0013] FIG. 2 is an enlarged schematic sectional view through the
turbine blade of FIG. 1, taken on lines 2-2;
[0014] FIG. 3 is a schematic sectional view like that of FIG. 2,
illustrating another embodiment; and
[0015] FIG. 4 is a block flow diagram of an approach for preparing
a coated gas turbine airfoil.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIG. 1 depicts a component article of a gas turbine engine
such as a turbine blade or turbine vane, and in this illustration a
turbine blade 20. The turbine blade 20 is formed of any operable
material, but is preferably a nickel-base superalloy. The turbine
blade 20 includes an airfoil section 22 against which the flow of
hot exhaust gas is directed. (The turbine vane or nozzle has a
similar appearance in respect to the pertinent airfoil section, but
typically includes other end structure to support the airfoil.) The
turbine blade 20 is mounted to a turbine disk (not shown) by a
dovetail 24 which extends downwardly from the airfoil 22 and
engages a slot on the turbine disk. A platform 26 extends
longitudinally outwardly from the area where the airfoil 22 is
joined to the dovetail 24. Optionally, a number of internal
passages extend through the interior of the airfoil 22, ending in
openings 28 in the surface of the airfoil 22. During service, a
flow of cooling air is directed through the internal passages to
reduce the temperature of the airfoil 22.
[0017] FIG. 2 is a sectional view through a portion of a portion of
the turbin blade 20, here the airfoil section 22. The turbine blade
20 has a body that serves as a substrate 30 with a surface 32.
Overlying and contacting the surface 32 is a protective structure
33 including a protective coating 34 comprising aluminum. The
protective coating 34 overlies the surface of the substrate 30 and
may be of any operable type. Several types of protective coating 34
are known in the art.
[0018] The protective coating 34 may be a diffusion aluminide that
initially includes only aluminum and elements diffused into the
protective coating 34 from the substrate 30, or is a modified
diffusion aluminide that initially includes other elements such as
platinum, chromium, or hafnium. In the simple diffusion aluminide,
aluminum is deposited onto the surface 32 and interdiffused with
the elements of the substrate 30. The modified diffusion aluminide
may be formed by depositing a layer of another element, such as
platinum, onto the surface 32, and then depositing the aluminum
layer (either pure aluminum or doped with a modifying element)
overlying the layer of the other element. The layers are
interdiffused with the material of the substrate. In these cases,
the aluminum layer may contain a modifying element such as hafnium,
yttrium, zirconium, chromium, or silicon, or combinations
thereof.
[0019] The protective coating 34 may instead be an MCrAlX overlay
coating. The terminology "MCrAlX" is a shorthand term of art for a
variety of families of overlay protective coatings 34 that may be
employed as environmental coatings or bond coats in thermal barrier
coating systems. In this and other forms, M refers to nickel,
cobalt, iron, and combinations thereof. In some of these protective
coatings, the chromium may be omitted. The X denotes elements such
as hafnium, zirconium, yttrium, tantalum, rhenium, platinum,
silicon, titanium, boron, carbon, and combinations thereof.
Specific compositions are known in the art. Some examples of MCrAlX
compositions include NiAlCrZr (as disclosed in U.S. Pat. No.
6,153,313) and NiAlZr (as disclosed in U.S. Pat. No. 6,255,001),
but this listing of examples is not to be taken as limiting.
[0020] The protective coating 34 is preferably from about 0.0005 to
about 0.005 inch thick, but thicker or thinner protective coatings
are operable.
[0021] For any of these types of protective coatings 34, an upper
surface 36 of the protective coating 34 oxidizes to form an
adherent aluminum oxide scale 38. The aluminum oxide scale 38 is
considered to be part of the protective coating 34. This aluminum
oxide scale 38 is quite thin, desirably on the order of about
0.0001 to about 0.0002 inch in thickness.
[0022] Overlying and contacting the protective coating 34 (and the
aluminum oxide scale 38 as well) is an oxygen barrier layer 40. The
oxygen barrier layer 40 comprises at least about 70 percent by
weight iridium, and most preferably is from about 70 to about 90
percent by weight iridium. If the oxygen barrier layer 40 has less
than about 70 percent by weight iridium (near the aluminum-iridium
eutectic point), the oxygen-barrier properties of the iridium
become too diluted and the oxygen-barrier effectiveness is
degraded, and the melting point of the oxygen barrier layer 40 is
reduced so that it is prone to melting in service. If the oxygen
barrier layer 40 is more than about 90 percent by weight iridium,
and particularly for pure iridium, the high-iridium material is
subject to vaporization in air at temperatures above about 1390K.,
near the service temperature of the protected article.
[0023] The oxygen barrier layer 40 preferably has a thickness of
from about 5 to about 50 micrometers. If the oxygen barrier layer
40 is thinner than about 5 micrometers, it does not impart
sufficient oxygen impermeability. If the oxygen barrier layer 40 is
thicker than about 50 micrometers, it tends to prevent sufficient
oxygen from reaching the protective layer to form the aluminum
oxide scale 38 and is also wasteful of the expensive element
iridium.
[0024] FIG. 3 is a schematic sectional view like that of FIG. 2,
illustrating another embodiment. (FIGS. 2 and 3 are not drawn to
scale.) The structure of FIG. 3 is like that of FIG. 2, and the
prior description is incorporated here, except that a ceramic
thermal barrier coating 42 overlies and contacts the oxygen barrier
layer 40. The ceramic thermal barrier coating 42 is preferably from
about 0.003 to about 0.010 inch thick, most preferably about 0.005
inch thick. The ceramic thermal barrier coating 42 is preferably
yttria-stabilized zirconia, which is zirconium oxide containing
from about 3 to about 12 weight percent, preferably from about 4 to
about 8 weight percent, of yttrium oxide. Other operable ceramic
materials may be used as well. The ceramic thermal barrier coating
42 may be deposited by any operable technique, such as electron
beam physical vapor deposition or plasma spray.
[0025] FIG. 4 is a block flow diagram of a preferred method for
practicing the invention. An article substrate is provided, numeral
50. The article is preferably a component of a gas turbine engine
such as a gas turbine blade or vane (or "nozzle", as the vane is
sometimes called). The article is most preferably made of a
nickel-base superalloy. As used herein, "nickel-base" means that
the composition has more nickel present than any other element. The
nickel-base superalloys are typically of a composition that is
strengthened by the precipitation of gamma-prime phase. The
preferred nickel-base alloy has a composition, in weight percent,
of from about 4 to about 20 percent cobalt, from about 1 to about
10 percent chromium, from about 5 to about 7 percent aluminum, from
0 to about 2 percent molybdenum, from about 3 to about 8 percent
tungsten, from about 4 to about 12 percent tantalum, from 0 to
about 2 percent titanium, from 0 to about 8 percent rhenium, from 0
to about 6 percent ruthenium, from 0 to about 1 percent niobium,
from 0 to about 0.1 percent carbon, from 0 to about 0.01 percent
boron, from 0 to about 0.1 percent yttrium, from 0 to about 1.5
percent hafnium, balance nickel and incidental impurities.
[0026] A most preferred alloy composition is Ren N5, which has a
nominal composition in weight percent of about 7.5 percent cobalt,
about 7 percent chromium, about 6.2 percent aluminum, about 6.5
percent tantalum, about 5 percent tungsten, about 1.5 percent
molybdenum, about 3 percent rhenium, about 0.05 percent carbon,
about 0.004 percent boron, about 0.15 percent hafnium, up to about
0.01 percent yttrium, balance nickel and incidental impurities.
Other operable superalloys include, for example, Ren N6, which has
a nominal composition in weight percent of about 12.5 percent
cobalt, about 4.2 percent chromium, about 1.4 percent molybdenum,
about 5.75 percent tungsten, about 5.4 percent rhenium, about 7.2
percent tantalum, about 5.75 percent aluminum, about 0.15 percent
hafnium, about 0.05 percent carbon, about 0.004 percent boron,
about 0.01 percent yttrium, balance nickel and incidental
impurities; Ren 142, which has a nominal composition, in weight
percent, of about 12 percent cobalt, about 6.8 percent chromium,
about 1.5 percent molybdenum, about 4.9 percent tungsten, about 6.4
percent tantalum, about 6.2 percent aluminum, about 2.8 percent
rhenium, about 1.5 percent hafnium, about 0.1 percent carbon, about
0.015 percent boron, balance nickel and incidental impurities;
CMSX-4, which has a nominal composition in weight percent of about
9.60 percent cobalt, about 6.6 percent chromium, about 0.60 percent
molybdenum, about 6.4 percent tungsten, about 3.0 percent rhenium,
about 6.5 percent tantalum, about 5.6 percent aluminum, about 1.0
percent titanium, about 0.10 percent hafnium, balance nickel and
incidental impurities; CMSX-10, which has a nominal composition in
weight percent of about 7.00 percent cobalt, about 2.65 percent
chromium, about 0.60 percent molybdenum, about 6.40 percent
tungsten, about 5.50 percent rhenium, about 7.5 percent tantalum,
about 5.80 percent aluminum, about 0.80 percent titanium, about
0.06 percent hafnium, about 0.4 percent niobium, balance nickel and
incidental impurities; PWA1480, which has a nominal composition in
weight percent of about 5.00 percent cobalt, about 10.0 percent
chromium, about 4.00 percent tungsten, about 12.0 percent tantalum,
about 5.00 percent aluminum, about 1.5 percent titanium, balance
nickel and incidental impurities; PWA1484, which has a nominal
composition in weight percent of about 10.00 percent cobalt, about
5.00 percent chromium, about 2.00 percent molybdenum, about 6.00
percent tungsten, about 3.00 percent rhenium, about 8.70 percent
tantalum, about 5.60 percent aluminum, about 0.10 percent hafnium,
balance nickel and incidental impurities; and MX-4, which has a
nominal composition as set forth in U.S. Pat. No. 5,482,789, in
weight percent, of from about 0.4 to about 6.5 percent ruthenium,
from about 4.5 to about 5.75 percent rhenium, from about 5.8 to
about 10.7 percent tantalum, from about 4.25 to about 17.0 percent
cobalt, from 0 to about 0.05 percent hafnium, from 0 to about 0.06
percent carbon, from 0 to about 0.01 percent boron, from 0 to about
0.02 percent yttrium, from about 0.9 to about 2.0 percent
molybdenum, from about 1.25 to about 6.0 percent chromium, from 0
to about 1.0 percent niobium, from about 5.0 to about 6.6 percent
aluminum, from 0 to about 1.0 percent titanium, from about 3.0 to
about 7.5 percent tungsten, and wherein the sum of molybdenum plus
chromium plus niobium is from about 2.15 to about 9.0 percent, and
wherein the sum of aluminum plus titanium plus tungsten is from
about 8.0 to about 15.1 percent, balance nickel and incidental
impurities. The use of the present invention is not limited to
these preferred alloys, and has broader applicability.
[0027] The protective coating 34 is applied, numeral 52. In the
preferred case of a diffusion aluminide protective coating 34, the
aluminum layer is deposited by any operable approach, with vapor
deposition preferred. In that approach, a hydrogen halide activator
gas, such as hydrogen chloride, is contacted with aluminum metal or
an aluminum alloy to form the corresponding aluminum halide gas.
Any modifying elements may be doped into the aluminum layer from a
corresponding gas, if desired. The aluminum halide gas contacts the
substrate 30, depositing the aluminum thereon. The deposition
occurs at elevated temperature such as from about 1825.degree. F.
to about 1975.degree. F. so that the deposited aluminum atoms
interdiffuse into the substrate 30 during a 4 to 20 hour cycle.
This technique allows alloying elements to be deposited into the
aluminum layer if desired, from the halide gas.
[0028] If the protective coating is a platinum (or palladium or
rhodium) aluminide, a first coating layer is deposited onto the
surface 32 of the substrate 30 before the aluminum layer is
deposited. This first coating is preferably accomplished by
electrodeposition. For the preferred platinum deposition, the
deposition is preferably accomplished by placing a
platinum-containing solution into a deposition tank and depositing
platinum from the solution onto the substrate 30. An operable
platinum-containing aqueous solution is Pt(NH.sub.3).sub.4HPO.sub.4
having a concentration of about 4-20 grams per liter of platinum,
and the voltage/current source is operated at about 1/2-10 amperes
per square foot of facing article surface. The platinum first
coating layer, which is preferably from about 1 to about 6
micrometers thick and most preferably about 5 micrometers thick, is
deposited in 1-4 hours at a temperature of 190-200.degree. F.
[0029] In the case of the MCrAlX overlay protective coating 34, the
protective coating 34 is deposited by any operable physical vapor
deposition technique, such as sputtering, cathodic arc or electron
beam, or any plasma spray technique such as atmospheric plasma
spray (APS) or low pressure plasma spray (LPPS).
[0030] The oxygen barrier layer 40 is deposited overlying and
contacting the protective coating 34 (including its aluminum oxide
scale 38), numeral 54. An iridium layer is preferably deposited by
electrodeposition. Electroplating techniques for depositing iridium
layers are known in the art for other purposes and are disclosed,
for example, in U.S. Pat. Nos. 4,721,551 and 3,639,219, whose
disclosures are incorporated by reference. The iridium layer is
preferably pure iridium, but it may be an iridium-containing
alloy.
[0031] After the iridium layer is deposited, it and the underlying
structure are typically heat treated, numeral 56, to interdiffuse
the elements of the iridium layer, the protective coating 34, and
the substrate 30. The resulting oxygen barrier layer 40 includes
iridium, preferably in an amount of from about 70 to about 90
percent by weight, with the balance elements diffused into the
oxygen barrier layer from the protective coating and the substrate,
such as nickel and aluminum. A preferred heat treatment is from
about 4 to about 16 hours at a temperature of from about
1800.degree. F. to about 2000.degree. F., in a non-oxidizing
atmosphere.
[0032] The ceramic thermal barrier coating 42 is optionally
applied, numeral 58. The application of the ceramic thermal barrier
coating is preferably accomplished by electron beam physical vapor
deposition or plasma spray.
[0033] Although a particular embodiment of the invention has been
described in detail for purposes of illustration, various
modifications and enhancements may be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is not to be limited except as by the appended claims.
* * * * *